Due to financial problems, the boarding-school of Saint-Loup is on the verge of closing its doors. In desperation, Jacquelin, the headmaster, has the idea to invite former students to a fund-raising reunion. Among the alumni, three men whose common point is to have been in love at the time with the headmaster's niece. One is a banker, the second a priest and the last one a globetrotter. All of a sudden, the peace of the assembly is disturbed: Jacquelin's niece has just been murdered.